The routing of flexible duct, the number of bends, the
degrees in each bend, and the amount of sag or
direction changes (snaking) allowed between support
joints will have serious effects on system performance
due to the increased resistance each introduces (See
Fig 6 & 7). Use the minimum length of flexible duct to
make connections (See Section 4.5). Excess length of
flexible duct shall not be installed to allow for possible
future relocations of air terminal devices.
Avoid installations where exposure to direct sunlight
can occur, e.g. turbine vents, sky lights, canopy
windows, etc. Prolonged exposure to sunlight will
cause degradation of the vapor barrier. Direct
exposure to UV light from a source lamp installed
within the HVAC system will cause degradation of
some inner core/liner materials.
Terminal devices shall be supported independently of
the flexible duct.
Repair torn or damaged vapor barrier/jacket with duct
tape listed and labeled to Standard UL 181B. If internal
core is penetrated, replace flexible duct or treat as a
connection.